1. Field of the Invention
The present invention relates to a soft tissue core biopsy instrument which is semi-automatic in operation. More specifically, the biopsy instrument of the present invention provides an instrument which can be operated using only one hand and which includes a cutting cannula which is caused to move in a snap action over a stylet which is manually advanced.
2. Description of the Prior Art
Heretofore, various soft tissue core biopsy instruments have been proposed.
The most well known instrument used in this procedure is manufactured by Travenol Laboratories of Deerfield, IL and is sold under the mark "TRU-CUT". This instrument enjoys 98% of the existing market. As disclosed in U.S. Pat. No. 3,477,423, the instrument comprises a two piece assembly; an outer cutting cannula mounted to one hub member and an inner stylet with a sampling notch ground into it mounted to a second hub, with the hubs being slidably interlocked. The instrument is assembled and placed into the body with the outer cutting cannula just to the rear of a lancet point or bevelled distal end of the stylet. Upon inserting the device up to or in front of the area to be biopsied, advancement of the assembly is halted. The stylet is manually advanced distally of the cannula with the cannula held stationery. Upon advancement of the stylet, the specimen notch is exposed. Tissue surrounding the stylet contracts into the specimen notch and the cutting cannula is then manually advanced distally over the stylet, slowly shearing off the tissue entrapped in the stylet's specimen notch. The instrument is then either (a) withdrawn and the stylet advanced distally to expose the tissue for preparation for study or (b) left in place and only the stylet is proximally removed from within the cannula so a determination of successful sampling may be made. If the sampling was not successful, the stylet may be reinserted into the cannula, which remains positioned within the patient, and a attempt to reposition the assembly of stylet and cannula and repeat sampling can be made.
Such technique using this basic design of a biopsy instrument is referred to as a manual technique. One drawback to the manual technique is that it requires a great deal of manual dexterity and motor coordination, along with the use of both hands, to advance the stylet while maintaining the position of the cannula and then to maintain the position of the stylet while advancing the cannula.
Another drawback is that the cannula is advanced relatively slowly, resulting in an extremely poor cutting action and allowing the surrounding tissue an opportunity to collapse, thus making no use of the stored kinetic energy in the material being severed.
The Beraha U.S. Pat. No. 4,600,014 discloses a transrectal prostate biopsy device which comprises a handle held in a physician's palm, and a guide tube extending forwardly of the handle. A cannula is slidably disposed within the guide tube and is movable from within the guide tube forwardly out of the distal end of the guide tube. A sampling stylet is telescopically disposed within the cannula and projects from the rear of the handle. A knob is provided at the proximal end of the stylet for extending a distal end of the stylet out of the distal end of the guide tube to expose a sampling thereon. The physician holds the handle in one hand using his index finger at the distal end of the guide tube to guide the instrument to a selected transrectal point on the prostate. Upon locating the point, the one hand holds the instrument steady while the other hand pushes the stylet forward and then pushes the cannula over the stylet to sever the tissue within the sampling slot. The device is then withdrawn to gain access to the sample. In one embodiment of the device, the cannula, when in the retracted position, is spring loaded by means fo a compressed spring. A release lever, which works against the compressed spring can be activated to release compression of the spring which then expands and pushes the cannula outwardly over the stylet.
This instrument, as stated, requires two handed operation. Also, since the stylet is not removable proximally from within the handle, the entire instrument must be withdrawn to obtain access to the sample.
Within the last two years, a fully automatic instrument manufactured by Radiplast, Inc. of Sweden has been introduced and is described in U.S. Pat. No. 4,699,154. This instrument comprises a reusable, spring-loaded box-shaped housing or handpiece, which activates a disposable cannula and stylet set. Both the stylet and cannula are activated in rapid succession.
The instrument has the advantage of eliminating the dexterity and motor coordination necessary in use of manual devices and also eliminates the slow cutting action of the manually advanced cannula and replaced it with a very quick, clean cut. This instrument, however, also has its drawbacks.
First, the reusable handpiece is very large, heavy, cumbersome, and expensive. Its weight and the awkwardness in using same preclude it from being used with imaging equipment other than ultrasound, inasmuch as it must be inserted into the body with the user maintaining control of the handpiece at all times. Thus, the patient cannot be imaged with many conventional radiographic apparatus, such as CAT scanners. A further drawback is encountered in automatically activating both the stylet and the cannula, as opposed to activating the stylet manually, in that the rapid speed at which the cannula follows the stylet into the tissue does not allow much tissue to collapse into the specimen notch, limiting the size of the sample.
Also, it does not allow imaging of the device with the stylet and sampling notch in the actual tissue to be sampled and further, since a handpiece is utilized, the user cannot remove the stylet proximally from within the instrument to inspect the sampling and the entire instrument must be removed to obtain access to the sampling, so that, if a repeat sampling is required, the entire instrument must be reinserted. Also, since the handpiece is reuseable, additional costs above the purchase price are involved in cleaning, maintenance, and maintaining sterility of the handpiece.
The semi-automatic soft tissue core biopsy instrument of the present invention, as will be described in greater detail hereinafter, is completely disposable, lightweight and inexpensive. Further, it allows the user to advance the stylet manually, and then rapidly advance the cutting cannula automatically, all with one hand. Also, since the stylet is removable from the proximal end of the instrument, the position of the cannula within the body need not be disturbed if a repeat biopsy is required.